The scenes in which Mona the monkey imitates Victor Lundin's agonized gestures whenever the alien masters activated the slave bracelets were not something the monkey was taught to do. It began to imitate the actor during these scenes, and the director decided to film these moments.
The "air pills" were stock M&Ms, while the "poi sausages" harvested from the Martian plants were pepperonis.
Paul Mantee and Victor Lundin were both convinced that the work they had done on this ambitious and imaginative film would provide a substantial boost to their careers. However, the lackluster distribution that Paramount gave the film, along with the poor box office performance, caused both actors' careers to suffer severe lags for years afterwards. Mantee, in fact, said that he didn't work again as an actor for 11 months.
The snow was real in the scene where Kit and Friday were buried after the meteorite impacts the Martian North pole. Paul Mantee states in the DVD commentary that they had to stay under the snow and breathe through straws for quite a long time whilst the camera set-ups were completed--an experience he found very unpleasant. After Victor Lundin digs Mantee out, his jaw and lower lip can be seen trembling from the cold in the next shot.